The present invention relates generally to a method of improving chromatography using microwave radiation. More particularly, the present invention relates to a method of improving chromatography of a fluid containing an analyte by the use of microwave-induced dielectric polarization.
There are three major chromatographic techniques: high performance liquid chromatography (HPLC), supercritical fluid chromatography (SFC), and gas chromatography (GC). The speed of these separation methods increases in the order GC greater than SFC greater than HPLC. The reason for this being the differences in the diffusivities of the respective mobile phases, and hence, of the analytes within the mobile phases. This difference in speed is especially notable with open-tubular columns. Open-tubular columns with internal diameters in the range of 0.25 to 0.53 mm are typically used for gas chromatography; however, these same columns would result in excessively long analysis times with either SFC or HPLC. This can be offset by using columns of narrower ID: hence open-tubular SFC and HPLC are typically done with columns of 0.04 to 0.05 mm ID. Even then, analysis is slow and these narrow ID columns present several additional difficulties. They have a very low capacity for analyte material, the volume of sample that can be injected is limited which lessens the mass sensitivity, and very small volume detector cells need to be used. It is for these reasons that open-tubular columns are seldom used for HPLC or SFC.
This is unfortunate as open-tubular columns have many inherent advantages over packed columns including better efficiency due to the lack of Eddy diffusion and the smaller stationary phase film thickness. The smaller volume of mobile phase typically used with open-tubular column separations results in sharper chromatographic peaks, further increasing efficiency and allowing for better sensitivity. The lower mobile phase flow rates of these columns also make it easier to interface with ionization type detectors: most importantly mass spectrometers. Finally, open-tubular columns have a much smaller pressure drop across them, allowing longer columns to be used.
As stated above, much faster analysis is possible with gas chromatography. However, the downside of gas chromatography is that the mobile phase has no solvating power and, therefore, only analytes that possess some volatility can be separated by the technique. Supercritical fluid chromatography can separate a wider range of analytes as the mobile phase has some solvating power. However, liquid chromatography is by far the most versatile chromatographic method. Virtually all analytes are amenable to liquid chromatography including macromolecules such as synthetic polymers, proteins, and carbohydrates.
If it were possible to increase the diffusivity of a liquid mobile phase, the resulting technique would offer the best of both worlds. The high diffusivity would allow for faster analysis and would make it possible to reap the benefits offered by open-tubular columns (of moderate to large internal diameters). However the liquid would still possess its high solvating power, making it possible to separate virtually any analyte. Previously, this has been accomplished by conducting liquid chromatography at highly elevated temperatures (up to 150xc2x0 C.). However, there are several disadvantages to this approach. First, the mobile phase must be preheated prior to reaching the column by passing through a certain length of tubing, maintained in an oven. There is a delay associated with this. In order that fast analysis could still be obtained, the analytes were delivered by a separate linexe2x80x94much shorter and with a narrower IDxe2x80x94that teed into the mobile phase line. Hence, there was a significant dilution of the analytes resulting in a loss of efficiency and sensitivity. Secondly, additional hardware was required in order to maintain pressure in the column so that the solvents did not boil at the elevated temperatures and also to cool the mobile phase down prior to reaching the detector. Thirdly, the analyst is limited in the types of stationary phases that can be used. Lastly, this approach will be problematic if working with analytes that are not temperature stable.
It is a desideratum of the present invention to avoid the animadversions of the above-mentioned existing techniques.
The present invention provides a novel and unique method of improving chromatography of a fluid containing an analyte, comprising the steps of: commencing a run of said fluid containing said analyte through a chromatoghaphic separation column; and subjecting said fluid containing said analyte to microwave radiation.
It is an object of the present invention to provide a more desirable approach to elevating the diffusivity of a liquid mobile phase than has been used previously. That is, to make use of the phenomenon of microwave-induced dielectric polarization.
This object and other features and advantages of the present invention will become apparent to those persons skilled in this particular area of technology and to others after reading the present patent application.